Oh man...if it wouldn't take me so long to obfuscate it. It's a normal query using cte to gather some values of 3 joined tables and the results get aggregated. I optimized the query over a long time playing around with different indexes and rewrote the query using different approaches. So the query is optimal with it's 300 ms. But sometimes the query takes 8000 ms allthough there's almost no load on the server. So I wanted to know if you got practical experiences with this behaviour?